Analysis Of Combined Heat Transfer Research Articles

Improving Cooling Capacity of Condensation-Free Radiant Cooling for Low-Emissivity Chilled Ceiling via Adaptive Double-Skin Infrared Membranes

Radiant cooling has well been acknowledged as energy efficient and thermal comfortable technology compared to conventional convective cooling. However, the radiant cooling exists two serious problems (viz., insufficient cooling capacity and high condensation risk) especially in hot and humid climate zones. By adding double-skin infrared transparent membranes (DIMs) onto radiant cooling panel, the air-contact surface can be separated from the cooling source surface, which makes it possible to use a low-temperature cooling source while maintaining air-contact surface higher than dew point temperature. The DIMs are transparent to radiant heat transfer which yields great cooling capacity while chilled ceiling has high emissivity (e.g., above 0.9). However, for metal chilled ceilings having low emissivity, radiant heat from cooling load to chilled ceiling would be reduced through DIMs, which results in insufficient cooling capacity. In this paper, a type of adaptive double-skin infrared membranes (a-DIMs) consisting a high-emissivity membrane and a high transparent membrane is proposed to improve cooling capacity of conventional metal chilled ceilings. The high-emissivity membrane serves as radiant cooling surface instead of low-emissivity chilled ceiling so as to improve radiant heat flux, while the high transparent membrane permits great radiant heat from cooling load to chilled ceiling. A combined heat transfer analysis based on semi-transparent surface radiation and natural convection were carried out to predict cooling capacity of condensation-free radiant cooling. The results indicate that the cooling capacity could be up to 101.9W/㎡ by adding a-DIMs consisting of a high-emissivity membrane of 0.96 and a high transparent membrane of 0.87, which is improved by 2 times compared to conventional metal chilled ceiling with low emissivity of 0.2. Moreover, the cooling capacity by adding a-DIMs is further improved by 25% compared to that by using both infrared transparent DIMs presented in our previous work. The results also indicate that the cooling capacity could be improved by above 2 times compared to conventional low-emissivity metal chilled ceiling by using the radiant cooling with a-DIMs for various humidity. It will be of great guidance for high-performance radiant cooling design without condensation and improved cooling capacity for low-emissivity metal chilled ceiling.

Evaluation of mesh dependence of combined heat transfer analysis method of radiation and convection field using OpenFOAM

Evaluation of mesh dependence of combined heat transfer analysis method of radiation and convection field using OpenFOAM

Natural element method study of combined natural convective and radiative heat transfer in irregular-shaped mediums with radiative properties

Numerical analysis of combined heat transfer in enclosures is of importance in thermal science. Among numerical approaches for the analysis of combined heat transfer, Natural Element Method (NEM) is well known as an efficient meshless technique, whose theory mainly based on natural Galerkin neighbors. The triangular medium is subjected to the simultaneous effect of natural convection fluid flow, conduction and radiation inside an absorbing, emitting, non-scattering and semi-transparent enclosure. Then, the concept of NEM is implemented for the discretization of mathematical governing equations within computational field. For radiation analysis, both P1 and Discrete Ordinate Method (DOM) are employed to determine the solution of Radiative Transfer Equation (RTE) through iterative procedure, which ultimately converges to final solutions that are then compared with analytical and numerical studies found in the literature. From the results, Natural Element Method shows its good performance on numerical heat transfer analysis of fluid flow problems.

Numerical simulation of conjugate conduction and natural convection heat transfer of nanofluid inside a square enclosure containing a conductive partition and several disconnected conducting solid blocks using the Buongiorno's two phase model

A two-dimensional numerical analysis of combined heat transfer (convection and conduction) in a nanofluid filled square enclosure is investigated using two phase method. Main attention was paid to the effects of the Rayleigh number (104≤Ra≤107), diameter (25nm≤dp≤145nm), volume fractions (0≤φ≤5%) and type of the nanoparticle (Cu, Al2O3, and TiO2), orientation of conductive wall, thermal conductivity ratio (0.2≤Kr≤25) and segmentation of conductive obstacle on the velocity, temperature fields and heat transfer characteristic. The results of this investigation showed that by adding several conductive obstacles inside the enclosure, the heat transfer rate decreases especially at low Ra. Moreover, it is found that, orientation of conductive partition has a big impact on the heat transfer rate at high Ra. It is also observed that in general, internal heating/cooling system has a considerably higher rate of the heat transfer compared with external ones. Finally, it is found that, the effect of the thermophoresis force is more pronounced for solid particles with low thermal conductivity like Al2O3 and especially TiO2.

Conjugate natural convection combined with surface thermal radiation in an air filled cavity with internal heat source

A two-dimensional numerical analysis of combined heat transfer (transient natural convection, surface thermal radiation and conduction) in an air filled square enclosure having heat-conducting solid walls of finite thickness and a local heat source in conditions of convective heat exchange with an environment has been carried out. The governing equations formulated in terms of the dimensionless stream function, vorticity and temperature have been numerically solved using the finite difference method. Particular efforts have been focused on the effects of five types of influential factors such as the Rayleigh number 104 ≤ Ra ≤106, the internal surface emissivity 0 ≤ ɛ < 1, the thermal conductivity ratio 1 ≤ k1,2 ≤ 1000, the ratio of solid wall thickness to cavity spacing 0.1 ≤ l/L ≤ 0.3 and the dimensionless time 0 ≤ τ ≤ 100 on the fluid flow and heat transfer. Comprehensive Nusselt numbers data are presented as functions of the governing parameters mentioned above.

Combined heat transfer of radiation and conduction in stacked radiation shields for vacuum insulation panels

Combined heat transfer of radiation and conduction considering depthwise conduction phenomena in stacked radiation shields for vacuum insulation panels (VIPs) having an artificial core structure is investigated. The purpose of this study is to establish a reliable analysis method for actual shield design. A one-dimensional problem is first analyzed. Actual two-dimensional problem is simplified for theoretical modeling and the depthwise conduction around contact spot is further considered. Test radiation shields are manufactured using press molding process with SUS 304 (AISI grade 304) plates, since this sample depicts the parametric effects well. Measurement of the effective thermal conductivity is performed with a VGHP apparatus. While various analytical and numerical models predict the effective thermal conductivity in the case of this specific specimen within about 40% error, the combined heat transfer analysis considering depthewise conduction phenomena is accurate within 10% error and it is thus recommended in estimating the effective thermal conductivity of stacked radiation shields.

Parallel ray tracing for radiative heat transfer

Notes that, in a full‐scale application of the Monte Carlo method for combined heat transfer analysis, problems usually arise from the large computing requirements. Here the method to overcome this difficulty is the parallel execution of the Monte Carlo method in a distributed computing environment. Addresses the problem of determination of the temperature field formed under the assumption of radiative equilibrium in an enclosure idealizing an industrial furnace. The medium contained in this enclosure absorbs, emits and scatters anisotropically thermal radiation. Discusses two topics in detail: first, the efficiency of the parallelization of the developed code, and second, the influence of the scattering behavior of the medium. The adopted parallelization method for the first topic is the decomposition of the statistical sample and its subsequent distribution among the available processors. The measured high efficiencies showed that this method is particularly suited to the target architecture of this study, which is a dedicated network of workstations supporting the message passing paradigm. For the second topic, the results showed that taking into account the isotropic scattering, as opposed to neglecting the scattering, has a pronounced impact on the temperature distribution inside the enclosure. In contrast, the consideration of the sharply forward scattering, that is characteristic of all the real combustion particles, leaves the predicted temperature field almost undistinguishable from the absorbing/emitting case.

Determination of Temperature Variable Properties of Composite Materials: Methodology and Experimental Results

In the present article we discuss a method for the determination of temperature variable properties of composite materials. The method involves thermophysical properties (specific heat and thermal conductivity) and rate of cure. The method is general and based on the combined analysis of heat transfer in thin and thick pieces of material. A simulation model is then developed to predict the cure response and heat transfer that occur in composite material during fabrication. It is validated by experimental results obtained with an epoxy resin/glass fiber composite.